1. Field of the Invention
The present invention relates to an impurity diffusion method, a substrate processing apparatus, and a method of manufacturing a semiconductor device.
2. Description of the Related Art
A transistor functions as an active device in a semiconductor device. Recently, many of highly integrated semiconductor devices have mounted therein a field effect transistor, for example, a metal oxide semiconductor field effect transistor (MOSFET), including a gate electrode for controlling turning-on/turning-off.
A gate electrode is formed by using a conductive material, and one of important factors with respect to the gate electrode is a work function thereof. Unless the work function of the gate electrode is controlled, a threshold value, for example, of the transistor may exceed a designed range, and thus, normal operations may not be performed.
If a gate electrode is formed by using polysilicon or amorphous silicon, a work function of the gate electrode is controlled by controlling an amount of a donor or accepter, which is so-called impurities, doped on the polysilicon or the amorphous silicon. Also, the amount of impurities doped on the polysilicon or the amorphous silicon affects a resistance value of the gate electrode.
As described above, since the amount of the doped impurities affects the work function and the resistance value of the gate electrode, the amount has to be strictly controlled. A technology of growing a film on which impurities are doped is disclosed in, for example, Patent Document 1.
In Patent Document 1, a surface of a substrate, that is, Si1 . . . xGex(100), is cleaned under a hydrogen atmosphere, and after that, a BCl3 gas is supplied with an inert gas that is H2 gas to grow a boron (B) layer of about one atomic layer thickness or less on the surface of the substrate. Then, a mixture gas of SiH4—GeH4—H2 is supplied to epitaxially grow a Si1 . . . xGex layer of a few to hundreds of nm.
In Patent Document 1, by repeatedly performing the growth of the B layer and the epitaxial growth of the Si1 . . . xGex layer, the Si1 . . . xGex layer on which boron, that is, an acceptor, is doped at a high concentration may be epitaxially grown on the surface of the substrate (for example, refer to paragraphs No. 0036 to 0040).
As described above, since the amount of the impurities doped on the polysilicon or the amorphous silicon forming the gate electrode affects the work function and the resistance value of the gate electrode, the amount of the impurities has to be strictly controlled.
Recently, along with the miniaturization of transistors, variations in the work function and the resistance value of the gate electrode caused by the impurities that are lost during surface oxidation or an etching process of the gate electrode have greatly increased, wherein the variations have not been apparent so far due to being excessively fine.
In order to compensate for the impurities lost during the surface oxidation or the etching process, it has suggested that impurities of a vapor phase are diffused toward the polysilicon or the amorphous silicon. However, it takes a long time by using vapor diffusion to diffuse the impurities to a high concentration. Thus, there is concern about degradation of throughput.
Also, Patent Document 1 discloses an epitaxial growth of a Si1 . . . xGex layer on which boron of a high concentration is doped. However, Patent Document 1 only discloses the Si1 . . . xGex layer doped with the high concentration boron, but does not teach a technology of compensating for lost impurities.    (Patent Document 1) Japanese Laid-open Patent Publication No. 2008-53605